1. Field of the Invention
This invention relates to tubular piston rods particularly for shock absorbers and spring devices of motor vehicles. A new structure of the piston rod and a new method for manufacturing such a piston rod are proposed. The new structure warrants a tight closure of the tubular piston rod on at least one end thereof and a rigid connection with other structural members to be connected with the piston rod. The new method is more economic than known methods for manufacturing such piston rods.
2. The Prior Art
According to German Utility Pat. No. 7 930 294 a tubular piston rod is proposed in which an extension of reduced diameter at a respective end is made by cold shaping or warm shaping. The extension of reduced diameter is intended to be connected to another structural member, e.g. a link member, by which a connection with the body of a motor vehicle is obtained. For improving the rigidity of such a tubular piston rod it is further known to fill the interior of the tube member with molten light metal. This has, however, the result that the weight of the piston rod is increased and the price of the piston rod becomes higher due to the increased manufacturing costs. If the piston rod is not filled with light metal, a further manufacturing step is necessary for closing at least one end of the piston rod in order to prevent escaping of the hydraulic of pneumatic damping fluid through the piston rod. In case of light-metal-filled piston rods, the interior of the piston rods can't be used as an additional working or compensation chamber.